This application is based on and claims priority to Japanese Patent Applications No. 2000-145987, filed May 18, 2000, No. 2000-145988, filed May 18, 2000, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates generally to a cooling system for an outboard motor, and more particularly to an improved cooling system for an exhaust system of an outboard motor.
2. Description of Related Art
An outboard motor typically comprises a power head including an internal combustion engine and a housing unit depending from the power head. The outboard motor, because of its compact nature, generally employs an exhaust system that includes an exhaust conduit in the housing unit and that exhausts through a submerged discharge port.
The conventional outboard motor also employs an open-loop cooling system that draws cooling water from the body of water in which the outboard motor is operated (e.g., a lake or an ocean) to primarily cool engine portions. The cooling water also is introduced into the exhaust system in order to cool the exhaust gases and the exhaust system through which the exhaust gases pass. The exhaust system then returns the cooling water to the body of water.
Usually, a majority of the cooling water that has run through cooling jackets within the engine is also used for cooling the exhaust system. This water has an increased temperature because the engine is extraordinary heated during operation. This heated water can come into contact with an inner surface of the housing unit such that heat is transferred to the housing unit. When the outboard motor is used in soft water environments, water containing a calcium (Ca) component contacts an outer surface of the housing unit. The calcium (Ca) component, when the housing unit is heated, discolors the housing unit to white. The discolored housing unit can deteriorate appearance of the outboard motor.
A need therefore exists for an improved cooling system for an outboard motor that can reduce heat transfer to a housing unit such that discoloring of the housing unit can be reduced.
When the outboard motor is used on the sea and sea water is employed for cooling the exhaust system, another problem can occur. The problem is that the exhaust gases produce sulfuric acid with the sea water that causes sulfuric acid corrosion of the housing unit.
Another need thus exists for an improved cooling system for an outboard motor that can inhibit a housing unit from causing sulfuric acid corrosion.
In accordance with one aspect of the present invention, an outboard motor comprises a power head including an internal combustion engine. A housing unit depends from the power head. An exhaust conduit is arranged to discharge exhaust gases from the engine. At least a portion of the exhaust conduit extends through the housing unit. A cooling system is arranged to cool at least the portion of the exhaust conduit by coolant. The cooling system includes an inner coolant pool surrounding the portion of the exhaust conduit. An outer coolant pool surrounds the inner coolant pool. The cooling system supplies the coolant to the inner and outer pools. The coolant supplied to the outer pool is cooler than the coolant supplied to the inner pool.
In accordance with another aspect of the present invention, an outboard motor comprises a power head including a four-cycle, internal combustion engine. A housing unit depends from the power head. A lubricant tank for the engine is disposed in the housing unit. An exhaust conduit is arranged to discharge exhaust gases from the engine. The exhaust conduit is disposed through the lubricant tank and at least a portion of the exhaust conduit extends lower than a bottom of the lubricant tank. A cooling system is arranged to cool at least the lubricant tank and the exhaust conduit by coolant. The cooling system includes an inner coolant pool surrounding the portion of the exhaust conduit. An outer coolant pool surrounds the inner coolant pool and the lubricant tank. The cooling system supplies the coolant to the inner and outer pools.
In accordance with a further aspect of the present invention, an outboard motor comprises a power head including an internal combustion engine. A housing unit depends from the power head. An exhaust system is arranged to discharge exhaust gases from the engine. The exhaust system includes an exhaust pipe connected to the engine and an expansion chamber disposed downstream of the exhaust pipe. The housing unit includes a tubular section to define a coolant pool that surrounds a portion of the exhaust pipe. The tubular section has a portion defining a bottom of the coolant pool. The portion of the tubular section is disposed in proximity to a top end of the expansion chamber.
In accordance with a still further aspect of the present invention, an outboard motor comprises a power head including an internal combustion engine. A housing unit depends from the power head. An exhaust system is arranged to discharge exhaust gases from the engine. The exhaust system includes an exhaust conduit having an outlet arranged to open to a space within the housing unit. The housing unit includes a portion forming a water pool surrounding the exhaust pipe. The housing unit defines a water discharge pathway through which the water in the water pool is discharged. The housing unit further defines a dividing wall separating the water discharge pathway from the space.